The effects of binary tidal forces on transport within an accretion disk are studied with a time-dependent hydrodynamical model of a two-dimensional isothermal accretion disk .
Tidal forces quickly truncate the accretion disk to radii of order half the average radius of the Roche lobe , and excite a two-armed spiral wave that remains stationary in the rotating reference frame of the binary system .
We measure an effective \alpha of order 0.1 near the outer edge of the disk in all of our models , independent of the mass ratio , Mach number , and radial density profile .
However , in cold disks with high Mach number , the effective \alpha drops rapidly with decreasing radius such that it falls below our threshold of measurement ( \sim 10 ^ { -3 } ) at a radius of only one third the tidal radius .
In warmer disks where the Mach numbers remain below 20 , we can measure an effective \alpha down to radii 10 times smaller than the maximum size of the disk .